The Tomato Magazine
Releases Expected Soon
Purple tomatoes, rich with health-promoting compounds,
may soon be available to commercial and home gardeners.
Oregon State University plant breeders hope to release the
first in a series of purple-skinned varieties in approximately two years,
according to Dr. Jim Myers, a professor of vegetable breeding
and genetics at Oregon State University, Corvallis, Ore.
First on the market will be saladette or smaller sized slicer tomatoes,
the researcher says. Crosses also are underway to come up
with purple-colored cherry and larger slicer and processing-types.
Began as a Research Project
History of OSU’s purple tomato work dates back to 2000, when
Myers okayed graduate student Carl Jones’ request to investigate
what could be done to enhance the health benefi ts of certain
vegetables. The decision was made to focus on tomatoes.
“At the time, we were looking primarily at carotenoids and
at some of the different genetic mutants that were available in
tomato,” Myers recalls. “By and by, Jones discovered a particular
gene, the anthocyanin fruit gene in tomatoes that produced a purple
The discovery was especially exciting due to the reported health
benefits of certain anthocyanin-rich foods, such as blueberries and
red grapes processed to produce wine.
and therapeutic roles in a number of human diseases. Through the
much publicized ‘French paradox,’ the public has become aware
that certain populations of red-wine drinkers in France and Italy
have much lower rates of coronary heart disease (CHD) than their
North American and Northern European counterparts. It is widely
accepted that red wine phenolics contribute at least partly to this
“The anthocyanin pigments of bilberries (Vaccinium
myrtillus) have long been used for improving visual acuity and
treating circulatory disorders,” Wrolstad continues. “There
experimental evidence that certain anthocyanins and fl avonoids
have anti-infl ammatory properties, and there are reports that orally
administered anthocyanins are benefi cial for treating diabetes
and ulcers and may have antiviral and antimicrobial activities. The chemical
basis for these desirable properties of fl avonoids is believed to be
related to their antioxidant capacity—their ability
to scavenge (clean away) and trap free radicals that damage
The specific anthocyanins present in OSU’s purple tomatoes are
mainly petunidin, but malvidin and delphinidin are also present,
Myers explains. The anthocyanins are modifi ed by the presence of
acyl (sugar) groups. Anthocyanins are a member of a larger class of
compounds called fl avonoids. Other members of this class include
quercetin, kaempferol, naringenin, catechin and isolfl avones.
Phenols or phenolics are related compounds that differ in basic
chemical structure but have similar function.
Although the current popular theory is that the health benefi ts of
anthocyanins are due to their antioxidant activity, recent research
suggests that anthocyanins may not act directly as antioxidants. The
thought is that they may produce health benefi ts in a more complex
manner, Myers notes.
Once Jones had completed his graduate work and moved
on, a second graduate student, Peter Mes, continued on under
Myers’ direction. Mes focused on trying to increase
the intensity of the purple pigment in
the fruit. While doing so,
he obtained other
that produced small
quantities of anthocyanin.
From there, he
and Myers concluded
that they could combine
these particular genes
and come up with a much
more intense color. In fact,
the fruit directly exposed to
sunlight throughout the growing
season developed skins
that were as dark purple as eggplant.
“These genes originate from
a wild species,” Myers says.“Anthocyanin fruit is derived from
a wild species, Solanum chilense.“The material we used originates
from a genetic stocks collection at the
University of California-Davis. It was
first developed by a Russian researcher
who back crossed it into cultivated
tomatoes from a wild species.”
There are a few quirks with consistency
of color yet to be worked out, Myers
“The purple pigment is only expressed in those portions of the
fruit that are exposed to sun light,” he details. “Where
the fruit is
shaded by a leaf or the calyx, or on the base of the fruit, when the
fruit ripens, it will turn a normal red color. We’d like to come
with types that exhibit purple skin all of the time—no matter what
the light conditions are.”
The other negative is the purple pigment is expressed only on
the skin. The interior of the fruit is red, Myers says. The hope is to
come up with a purple-fl eshed interior.
Greater Potential Benefits
While not there yet, the university’s purple-skinned tomatoes
do have anthocyanin. While the levels are about 1/10 to 1/20 of that
found in blueberries—blueberries are one of the richest sources
of anthocyanins known—Americans consume far more tomatoes
per year than blueberries. The potential health benefi ts could be
“In recent years, per capita consumption of tomatoes in the U.S.
is about 90 pounds per person per year,” Myers points out. “In
consumption of fresh and frozen blueberries per person per
year averages less than one pound.”
Does the presence of anthocyanin affect
the taste of the potential purple
“ Some of the lines with extremely high anthocyanin have a strong
flavor described as ‘inky,’” admits Myers’ current
graduate student, Peter Boches, adding that “Pure anthocyanin has
no flavor, so this may be a result of related changes in chemical composition.
We have evidence to suggest that at least one of the
genes involved is a regulatory gene that interacts with several biosynthetic
pathways; so multiple changes in the chemical composition of the tomato may have
taken place in order to accommodate the increased anthocyanin production, he
“The taste of tomatoes in the breeding program could also be influenced
by the presence of other ‘wild’ genes that were carried along on
the chromosome with the genes that activate anthocyanin production,” the
researcher theorizes. “By crossing extremely high anthocyanin lines with
tomato cultivars known for
their good taste, such as ‘Sungold,’ we have recovered
individual plants that produce tomatoes with
high amounts of anthocyanin and acceptable flavor.
We anticipate being able to produce stable lines with
good fl avor and moderate amounts of anthocyanin
from these individual plants or others like them.”
Meanwhile, the OSU professor is confident that
his graduate students have come up with a purple
tomato line that is distinctly different and has more to
offer than ‘Black Prince,’ ‘Purple Cherokee’ and other
so-called purple lines already on the market.
“All of the ‘black’ and ‘purple’ varieties that
we have examined in our fi eld trials have the green flesh
gene which prevents normal chlorophyll breakdown,
resulting in a brown compound called pheophytin,” Myers points out. “In
combination with pink or red color from the carotenoids normally found in tomato
fruit, a muddy brownish purple color is produced.The biochemical composition
of the tomatoes that we
have developed is fundamentally different.”
As for now, priority No. 1 is to release “a bunch” of varieties
within the next two years, Myers says. The first releases
will be small slicer and saladette types for the fresh market. Next
will be purple cherry tomato and larger slicer and processing types
to provide offerings for virtually every need.
Will purple tomatoes prove a hit with the public? That remains
to be seen, the researcher admits. Since news of the research at
OSU hit the press, however, inquiries have been pouring in from
all over the world. While most of the interest has come from home
gardeners, feedback also is coming in from fresh and processed
Funding for the OSU purple-tomato breeding program is
provided through an endowed chair. This has enabled Myers and
his graduate students to move forward without worrying about how
to cover their research costs.
Since the OSU tomato breeding program got under way in the
1950s, about 13 varieties have been released to the public, Myers
says. One of the better known varieties is Legend, a very early,
large late blight-resistant slicer type that has done well under
Oregon climatic conditions.
Editor’s note: Jim Myers can be contacted at firstname.lastname@example.org.
© 2006 Columbia
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